The effect of reaction conditions on the rheological behaviour of various polyurethane prepolymer as potting compound for fabrication of hollow fibre haemodialyzer has been studied by means of a Brookfield viscometer. Depending on the monomers used and reaction conditions, dilatant and pseudoplastic behaviour is noticed. Bulk polymerized prepolymers based on HDI/castor oil, SMDI/castor oil and HDI/polypropylene glycol exhibit pseudoplastic character, which are favourable for easy dispensibility, non-wicking and good dispersion in potting of hollow fibre.